NASA Finds Unusual Origins of High-Energy Electrons

NASA Finds Unusual Origins of High-Energy Electrons

High above the surface, Earth’s magnetic field constantly deflects incoming supersonic particles from the sun. These particles are disturbed in regions just outside of Earth’s magnetic field – and some are reflected into a turbulent region called the foreshock.

New observations from NASA’s THEMIS – short for Time History of Events and Macroscale Interactions during Substorms – mission show that this turbulent region can accelerate electrons up to speeds approaching the speed of light. Such extremely fast particles have been observed in near-Earth space and many other places in the universe, but the mechanisms that accelerate them have not yet been concretely understood.

The new results provide the first steps towards an answer, while opening up more questions. The research finds electrons can be accelerated to extremely high speeds in a near-Earth region farther from Earth than previously thought possible – leading to new inquiries about what causes the acceleration. These findings may change the accepted theories on how electrons can be accelerated not only in shocks near Earth, but also throughout the universe. Having a better understanding of how particles are energized will help scientists and engineers better equip spacecraft and astronauts to deal with these particles, which can cause equipment to malfunction and affect space travelers.

“This affects pretty much every field that deals with high-energy particles, from studies of cosmic rays to solar flares and coronal mass ejections, which have the potential to damage satellites and affect astronauts on expeditions to Mars,” said Lynn Wilson, lead author of the paper on these results at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The results, published in Physical Review Letters, on Nov. 14, 2016, describe how such particles may get accelerated in specific regions just beyond Earth’s magnetic field. Typically, a particle streaming toward Earth first encounters a boundary region known as the bow shock, which forms a protective barrier between the solar wind, the continuous and varying stream of charged particles flowing from the sun, and Earth. The magnetic field in the bow shock slows the particles, causing most to be deflected away from Earth, though some are reflected back towards the sun. These reflected particles form a region of electrons and ions called the foreshock region.

This image represents one of the traditional proposed mechanisms for accelerating particles across a shock, called a shock drift acceleration. The electrons (yellow) and protons (blue) can be seen moving in the collision area where two hot plasma bubbles collide (red vertical line). The cyan arrows represent the magnetic field and the light green arrows, the electric field. Credits: NASA Goddard's Scientific Visualization Studio/Tom Bridgman, data visualizer

This image represents one of the traditional proposed mechanisms for accelerating particles across a shock, called a shock drift acceleration. The electrons (yellow) and protons (blue) can be seen moving in the collision area where two hot plasma bubbles collide (red vertical line). The cyan arrows represent the magnetic field and the light green arrows, the electric field.
Credits: NASA Goddard’s Scientific Visualization Studio/Tom Bridgman, data visualizer

Some of those particles in the foreshock region are highly energetic, fast moving electrons and ions. Historically, scientists have thought one way these particles get to such high energies is by bouncing back and forth across the bow shock, gaining a little extra energy from each collision. However, the new observations suggest the particles can also gain energy through electromagnetic activity in the foreshock region itself.

The observations that led to this discovery were taken from one of the THEMIS – short for Time History of Events and Macroscale Interactions during Substorms – mission satellites. The five THEMIS satellites circled Earth to study how the planet’s magnetosphere captured and released solar wind energy, in order to understand what initiates the geomagnetic substorms that cause aurora. The THEMIS orbits took the spacecraft across the foreshock boundary regions. The primary THEMIS mission concluded successfully in 2010 and now two of the satellites collect data in orbit around the moon.

Operating between the sun and Earth, the spacecraft found electrons accelerated to extremely high energies. The accelerated observations lasted less than a minute, but were much higher than the average energy of particles in the region, and much higher than can be explained by collisions alone. Simultaneous observations from the additional Heliophysics spacecraft, Wind and STEREO, showed no solar radio bursts or interplanetary shocks, so the high-energy electrons did not originate from solar activity.

“This is a puzzling case because we’re seeing energetic electrons where we don’t think they should be, and no model fits them,” said David Sibeck, co-author and THEMIS project scientist at NASA Goddard. “There is a gap in our knowledge, something basic is missing.”

The electrons also could not have originated from the bow shock, as had been previously thought. If the electrons were accelerated in the bow shock, they would have a preferred movement direction and location – in line with the magnetic field and moving away from the bow shock in a small, specific region. However, the observed electrons were moving in all directions, not just along magnetic field lines. Additionally, the bow shock can only produce energies at roughly one tenth of the observed electrons’ energies. Instead, the cause of the electrons’ acceleration was found to be within the foreshock region itself.

“It seems to suggest that incredibly small scale things are doing this because the large scale stuff can’t explain it,” Wilson said.

High-energy particles have been observed in the foreshock region for more than 50 years, but until now, no one had seen the high-energy electrons originate from within the foreshock region. This is partially due to the short timescale on which the electrons are accelerated, as previous observations had averaged over several minutes, which may have hidden any event. THEMIS gathers observations much more quickly, making it uniquely able to see the particles.

Next, the researchers intend to gather more observations from THEMIS to determine the specific mechanism behind the electrons’ acceleration.

Source: NASA

‘Nano-welding’ taken to the limits as specific bonds are cut and formed.

‘Nano-welding’ taken to the limits as specific bonds are cut and formed.

9 November 2012

Simon Hadlington

Electrons from a scanning tunnelling microscope have been used to selectively break an acetyl-sulfur bond © Wilson Ho

In a remarkable demonstration of the extreme limits of nanoscale engineering, researchers from the US and China have used the tip of a scanning tunnelling microscope (STM) to cleave and form selected chemical bonds on a complex molecule. The work marks another step along the road of ever-increasing control of single-molecule manipulations.

The team, led by veteran molecule manipulator Wilson Ho of the University of California, Irvine, designed a compound consisting of a chain of three aromatic rings with a tail at each end, comprising an acetyl group attached to the ring system by a sulfur. This molecule was then adsorbed to a nickel-aluminium surface and the tip of the STM was positioned over one of the ‘tail ends’ of the molecule. Electrons from the tip were injected into the sulfur–acetyl bond. At a particular threshold energy of the electrons, the bond snaps. ‘This occurs with surprisingly high efficiency,’ Ho says, with the energy being localised at the bond and with relatively little dissipation across the rest of the molecule.

Similarly, the bond between the sulfur and the aromatic ring can also be selectively cleaved at a given end of the molecule. By this method the researchers sequentially broke all four bonds, leaving the aromatic chain remaining. In a second series of experiments the team cleaved the acetyl groups, exposing the sulfurs. They deposited gold atoms onto the surface and gradually nudged them closer to the sulfurs with the STM tip. ‘Sometimes a bond forms, but sometimes it doesn’t,’ Ho says. By ‘energising’ the sulfur and the gold with electrons from the STM, a much higher rate of bond formation was achieved. ‘By exciting the gold and the sulfur, we can form a bond through a kind of “nano-welding” process,’ says Ho. The microscope was also able to image the patterns of electronic distribution as the various bonds formed and broke.


The team used 1,4-bis[4’-(acetylthio)styryl]benzene to test its ‘nano-welding’ technique

Other experts in the field recognise the significance of the new work. Geoff Thornton, of UCL and the London Centre for Nanotechnology, UK, says: ‘It’s a lovely piece of work.’ Thornton adds: ‘The modification of the molecular electronic structure on attaching a gold atom at both ends of the molecule is also fascinating, but I was left wondering what role the alloy substrate might play in this process.’

‘Ho’s team shows that the techniques that work on small and well-studied molecules also work beautifully on large extended chemical structures,’ says Peter Sloan of the University of Bath, UK. ‘Atomically engineered molecules probably won’t be appearing be appearing in the high-street soon, but these researchers have taken a small but important step.’


Y Jiang et al, Nat. Chem., 2012, DOI: 10.1038/nchem.1488

Editors note: Full article can be found here.

Credit:  ( Magazine )


The Riddle of Anti-Matter

The Riddle of Anti-Matter

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In high-res 1080p. Explores one of the deepest mysteries about the origin of our universe. According to standard theory, the early moments of the universe were marked by the explosive contact between subatomic particles of opposite charge. Featuring short interviews with Masaki Hori, Tokyo University and Jeffrey Hangst, Aarhus University.

Scientists are now focusing their most powerful technologies on an effort to figure out exactly what happened. Our understanding of cosmic history hangs on the question: how did matter as we know it survive? And what happened to its birth twin, its opposite, a mysterious substance known as antimatter?

A crew of astronauts is making its way to a launch pad at the Kennedy Space Center in Florida. Little noticed in the publicity surrounding the close of this storied program is the cargo bolted into Endeavor’s hold. It’s a science instrument that some hope will become one of the most important scientific contributions of human space flight.

It’s a kind of telescope, though it will not return dazzling images of cosmic realms long hidden from view, the distant corners of the universe, or the hidden structure of black holes and exploding stars.

Unlike the great observatories that were launched aboard the shuttle, it was not named for a famous astronomer, like Hubble, or the Chandra X-ray observatory.

The instrument, called the Alpha Magnetic Spectrometer, or AMS. The promise surrounding this device is that it will enable scientists to look at the universe in a completely new way.

Most telescopes are designed to capture photons, so-called neutral particles reflected or emitted by objects such as stars or galaxies. AMS will capture something different: exotic particles and atoms that are endowed with an electrical charge. The instrument is tuned to capture “cosmic rays” at high energy hurled out by supernova explosions or the turbulent regions surrounding black holes. And there are high hopes that it will capture particles of antimatter from a very early time that remains shrouded in mystery.

The chain of events that gave rise to the universe is described by what’s known as the Standard model. It’s a theory in the scientific sense, in that it combines a body of observations, experimental evidence, and mathematical models into a consistent overall picture. But this picture is not necessarily complete.

The universe began hot. After about a billionth of a second, it had cooled down enough for fundamental particles to emerge in pairs of opposite charge, known as quarks and antiquarks. After that came leptons and antileptons, such as electrons and positrons. These pairs began annihilating each other.

Most quark pairs were gone by the time the universe was a second old, with most leptons gone a few seconds later. When the dust settled, so to speak, a tiny amount of matter, about one particle in a billion, managed to survive the mass annihilation.

That tiny amount went on to form the universe we can know – all the light emitting gas, dust, stars, galaxies, and planets. To be sure, antimatter does exist in our universe today. The Fermi Gamma Ray Space Telescope spotted a giant plume of antimatter extending out from the center of our galaxy, most likely created by the acceleration of particles around a supermassive black hole.

The same telescope picked up signs of antimatter created by lightning strikes in giant thunderstorms in Earth’s atmosphere. Scientists have long known how to create antimatter artificially in physics labs – in the superhot environments created by crashing atoms together at nearly the speed of light.

Here is one of the biggest and most enduring mysteries in science: why do we live in a matter-dominated universe? What process caused matter to survive and antimatter to all but disappear? One possibility: that large amounts of antimatter have survived down the eons alongside matter.

In 1928, a young physicist, Paul Dirac, wrote equations that predicted the existence of antimatter. Dirac showed that every type of particle has a twin, exactly identical but of opposite charge. As Dirac saw it, the electron and the positron are mirror images of each other. With all the same properties, they would behave in exactly the same way whether in realms of matter or antimatter. It became clear, though, that ours is a matter universe. The Apollo astronauts went to the moon and back, never once getting annihilated. Solar cosmic rays proved to be matter, not antimatter.

It stands to reason that when the universe was more tightly packed, that it would have experienced an “annihilation catastrophe” that cleared the universe of large chunks of the stuff. Unless antimatter somehow became separated from its twin at birth and exists beyond our field of view, scientists are left to wonder: why do we live in a matter-dominated universe?